This kind of RF sputtering apparatus is known, e.g., in Patent Document 1. The apparatus in question is provided, inside a vacuum chamber, with a stage which holds a substrate to be subjected to processing in a state of leaving one surface thereof open and of being electrically insulated. Rare gas such as argon gas is introduced into the vacuum chamber that has been evacuated to a predetermined pressure. RF power is then applied to a target to thereby sputter the target, and the sputtered particles generated by the sputtering are caused to get adhered to, and deposited on, said one surface of the substrate, thereby forming a predetermined thin film.
It is to be noted here that, when the target is sputtered by applying RF power, self-bias potential is applied to the substrate that is held by the stage. It is generally known that, as a consequence, the ions and the like in the plasma of the rare gas are attracted toward the substrate and what has been deposited on the substrate will get sputtered, thereby giving rise to so-called reverse sputtering. Under the circumstances, if the amount of reverse sputtering increases, the rate of film forming will be lowered (the film-forming time becomes longer). As a consequence, it becomes important to suppress the amount of reverse sputtering to the best extent possible.